/**
 * flow 流加载组件
 */

layui.define('jquery', function (exports) {
  "use strict";

  var $ = layui.$, Flow = function (options) {
      }
      , ELEM_MORE = 'layui-flow-more'
      ,
      ELEM_LOAD = '<i class="layui-anim layui-anim-rotate layui-anim-loop layui-icon ">&#xe63e;</i>';

  //主方法
  Flow.prototype.load = function (options) {
    var that = this, page = 0, lock, isOver, lazyimg, timer;
    options = options || {};

    var elem = $(options.elem);
    if (!elem[0]) {
      return;
    }
    var scrollElem = $(options.scrollElem || document); //滚动条所在元素
    var mb = options.mb || 50; //与底部的临界距离
    var isAuto = 'isAuto' in options ? options.isAuto : true; //是否自动滚动加载
    var end = options.end || '没有更多了'; //“末页”显示文案

    //滚动条所在元素是否为document
    var notDocment = options.scrollElem && options.scrollElem !== document;

    //加载更多
    var ELEM_TEXT = '<cite>加载更多</cite>'
        , more = $(
        '<div class="layui-flow-more"><a href="javascript:;">' + ELEM_TEXT
        + '</a></div>');

    if (!elem.find('.layui-flow-more')[0]) {
      elem.append(more);
    }

    //加载下一个元素
    var next = function (html, over) {
      html = $(html);
      more.before(html);
      over = over == 0 ? true : null;
      over ? more.html(end) : more.find('a').html(ELEM_TEXT);
      isOver = over;
      lock = null;
      lazyimg && lazyimg();
    };

    //触发请求
    var done = function () {
      lock = true;
      more.find('a').html(ELEM_LOAD);
      typeof options.done === 'function' && options.done(++page, next);
    };

    done();

    //不自动滚动加载
    more.find('a').on('click', function () {
      var othis = $(this);
      if (isOver) {
        return;
      }
      lock || done();
    });

    //如果允许图片懒加载
    if (options.isLazyimg) {
      var lazyimg = that.lazyimg({
        elem: options.elem + ' img'
        , scrollElem: options.scrollElem
      });
    }

    if (!isAuto) {
      return that;
    }

    scrollElem.on('scroll', function () {
      var othis = $(this), top = othis.scrollTop();

      if (timer) {
        clearTimeout(timer);
      }
      if (isOver || !elem.width()) {
        return;
      } //如果已经结束，或者元素处于隐藏状态，则不执行滚动加载

      timer = setTimeout(function () {
        //计算滚动所在容器的可视高度
        var height = notDocment ? othis.height() : $(window).height();

        //计算滚动所在容器的实际高度
        var scrollHeight = notDocment
            ? othis.prop('scrollHeight')
            : document.documentElement.scrollHeight;

        //临界点
        if (scrollHeight - top - height <= mb) {
          lock || done();
        }
      }, 100);
    });

    return that;
  };

  //图片懒加载
  Flow.prototype.lazyimg = function (options) {
    var that = this, index = 0, haveScroll;
    options = options || {};

    var scrollElem = $(options.scrollElem || document); //滚动条所在元素
    var elem = options.elem || 'img';

    //滚动条所在元素是否为document
    var notDocment = options.scrollElem && options.scrollElem !== document;

    //显示图片
    var show = function (item, height) {
      var start = scrollElem.scrollTop(), end = start + height;
      var elemTop = notDocment ? function () {
        return item.offset().top - scrollElem.offset().top + start;
      }() : item.offset().top;

      /* 始终只加载在当前屏范围内的图片 */
      if (elemTop >= start && elemTop <= end) {
        if (item.attr('lay-src')) {
          var src = item.attr('lay-src');
          layui.img(src, function () {
            var next = that.lazyimg.elem.eq(index);
            item.attr('src', src).removeAttr('lay-src');

            /* 当前图片加载就绪后，检测下一个图片是否在当前屏 */
            next[0] && render(next);
            index++;
          }, function () {
            var next = that.lazyimg.elem.eq(index);
            item.removeAttr('lay-src');
          });
        }
      }
    }, render = function (othis, scroll) {

      //计算滚动所在容器的可视高度
      var height = notDocment ? (scroll || scrollElem).height() : $(
          window).height();
      var start = scrollElem.scrollTop(), end = start + height;

      that.lazyimg.elem = $(elem);

      if (othis) {
        show(othis, height);
      } else {
        //计算未加载过的图片
        for (var i = 0; i < that.lazyimg.elem.length; i++) {
          var item = that.lazyimg.elem.eq(i),
              elemTop = notDocment ? function () {
                return item.offset().top - scrollElem.offset().top + start;
              }() : item.offset().top;

          show(item, height);
          index = i;

          //如果图片的top坐标，超出了当前屏，则终止后续图片的遍历
          if (elemTop > end) {
            break;
          }
        }
      }
    };

    render();

    if (!haveScroll) {
      var timer;
      scrollElem.on('scroll', function () {
        var othis = $(this);
        if (timer) {
          clearTimeout(timer)
        }
        timer = setTimeout(function () {
          render(null, othis);
        }, 50);
      });
      haveScroll = true;
    }
    return render;
  };

  //暴露接口
  exports('flow', new Flow());
});
